I don't have a token idea, more of a caution and suggestion. For high level players, the charm slot is so tight: avarice, awakened synergy, and _free_. The charm necklace is out for most due to the legendaries. Bracelets are getting expensive and compete with guided strike (rogues, possibly people who use Thor's or any crit expanded weapon). So what gets used for the third charm? Greater onyx charm? Greater quicksilver? Quickstrike? Shadowshot? Questor's? Brooching? Spell swapping? Mad evoker's? Dracolich? Wil's dragonheart? Not to mention the rares with stat manipulation (sipquick, fiendish, etc.).
I'm a proponent for another charm expander (belt was mentioned, I like it, competes with some good ones). Additionally, I would be in favor of capping the total number of charms (8 is the limit right now, so maybe that's a good number).
Finally, I think the design space for charms in the UR level is saturated.